Zebra Stripes Confuse Flies

Zebra stripes confuse flies claim scientists in reports in BBC Nature News 9 February 2012, ABC News in Science 10 February 2012, and Journal of Experimental Biology, doi: 10.1242/jeb.070680. Scientists in Hungary and Sweden have carried out a series of experiments to see if the striped pattern of zebras has any advantage in protecting the animals from biting flies. They noticed that dark coloured horses were more attractive to tabanid flies (otherwise known as horseflies) than white horses and they found that dark horses reflected horizontally polarised light, and that is what attracted the flies. The researchers then wondered whether the black and white pattern on zebras would be more or less attractive to the flies. To test this they set up models with dark and light colours and striped patterns similar to zebra patterns in a field in Hungary to see which ones attracted the most flies. They found the dark models attracted the most flies, but the black and white striped models attracted as few or fewer flies than the white models.

The researcher wrote: “This work provides an experimentally supported explanation for the underlying mechanism leading to the selective advantage of a black-and-white striped coat pattern”. They concluded “that zebras have evolved a coat pattern in which the stripes are narrow enough to ensure minimum attractiveness to tabanid flies”. They also added: “The selection pressure for striped coat patterns as a response to blood-sucking dipteran parasites is probably high in this region [Africa]”. Not all scientists agree that this explains the origin of the zebra pattern. Matthew Cobb, an evolutionary biologist from the University of Manchester told BBC News: “Above all, for this explanation to be true, the authors would have to show that tabanid fly bites are a major selection pressure on zebras, but not on horses and donkeys found elsewhere in the world … none of which are stripy”.

3. If there was any way of selectively breeding striped horses farmers would be doing it.

4. In spite of their name, horseflies bite other animals and even chew on people – ouch don’t I know it!

Therefore, if this new evolutionary theory is correct, then fly infested countries should be populated by striped farmers riding striped horses out to inspect their striped cattle.

Matthew Cobb’s criticism is correct, but it does not get to the real issue of explaining the origin of the stripes. The real question is: how does being attacked by flies change the genes that control colour patterning in an animal’s skin? The scientists who did this experiment are correct in claiming there is a “selection pressure” for stripes in places where flies abound. However, that only works once the animals already have pigment and stripes. Avoiding flies is a useful characteristic when you already have stripes, but it does not explain how the characteristic came about.

Here is a good example of the difference between natural selection and evolution. Natural selection is a real ecological process, and explains why living things with certain characteristics survive in the environments they are found in. Evolution is supposed to be a story about how those characteristics came into being. It was Darwin who first confused and falsely equated the selection of an already existing characteristic with the selection being the explanation of how the characteristic came about, i.e. its origin. He was wrong then, and this equation is still wrong today. 153 years after Darwin’s book On the Origin of Species by Means of Natural Selection was published. It is time scientists and other academics applied some critical thinking to this issue and realise they have been bluffed by a theologian – Darwin, whose only formal qualifications were in theology, and whose anti-God theological agenda was the motivation behind his façade of science. (Ref. ecology, insects, pigmentation)